I think he is meant to stop approaching you but he wasn't included in the school groups so you couldn't greet him like the other school kids. I think this was breaking the remaining content and is fixed in the dev version.
Interesting. In all releases I've always been able to chat with him in the restroom along with the Gopniks. In v0.71 that's only the case
before the large cafeteria/locker room event.
Before v0.71, after that large cafeteria/locker room event which ends at Sonia's house I was always approached the next morning on the school grounds by a couple of students looking for a good time. After that Niko would still be outside of the school grounds with Artem, Katya, etc. every day, and if I approached him he would tell me about how he found someone to repair my reputation and I needed to go with him to the bar. Now, in my last few v0.71 games, the event before school never happens and Niko just completely vanishes so the whoring route never happens. I've tried looking everywhere for him, including the bar in the industrial area, but I can't find him.